Most rear wheel drive vehicles which are selectively engagable to be all wheel drive vehicles have a transfer case. The transfer case typically has a primary shaft which is connected to the output of a vehicle transmission. The primary shaft typically rotatably mounts a sprocket which engages with a chain. The chain typically engages with another sprocket which is typically connected with a secondary shaft. The secondary shaft is rotatably mounted within the transfer case. The secondary shaft is torsionally connected with a front drive shaft which is torsionally connected with a front differential to power front wheels of the vehicle. To provide a function of selectively engaging the front wheels of the vehicle, typically there is a clutch mechanism which selectively engages the sprocket on the primary shaft with the primary shaft to transfer torque to the primary shaft to the secondary shaft thereby selectively engaging the front wheels of the vehicle. When ideal pavement conditions exist, typically the clutch will not be engaged so that the vehicle only engages the rear wheels of the vehicle. A controller is typically provided which is cognizant of wheel slip conditions to automatically control the engagement of the clutch. In some embodiments, the clutch can also be engaged as a result of operator demand.
Most transfer cases have some type of lubricant pump to provide lubrication for the clutch in its associated friction pack. The operation of this pump provides a load on the vehicle engine either mechanically by being powered by the take off from the vehicle drive train or is a load upon the engine indirectly by generating a parasitic electrical load. It is desirable to provide a transfer case wherein the lubrication needed for the friction pack of the clutch can be provided in large manner or in total passively from the operation of the transfer case. An example of such a transfer case is provided in U.S. Pat. No. 7,753,173 to Gratzer et al. It is desirable to provide a transfer case that is an alternate to Gratzer et al.